1. Field Of The Invention
The present invention relates to the gradual replacement of ozone-damaging Freon 12.RTM. refrigerant with a refrigerant that is less damaging to the ozone layer in systems designed to use Freon 12.RTM.. More particularly the present invention relates to an improved refrigerant composition, method and apparatus for refrigeration wherein two non-Freon 12 refrigerants are mixed in a defined ratio such that the temperature-pressure relationship of the mix approximates that of ozone-damaging Freon 12.RTM., especially at high operating temperatures. The mixture is compatible with Freon 12.RTM. so that it can be added to supplement and gradually replace ozone-damaging Freon 12.RTM.. A further particularity of the instant invention relates to an improved method and apparatus for refrigeration wherein refrigerant mixture is mixed with a soluble lubricating oil to provide lubrication to the apparatus. The lubricant is soluble in both the mixture of the invention and Freon 12.RTM. refrigerant.
2. General Background
Until recently, R-12 or dichlorodifluoromethane ((hereinafter sometimes called "Freon 12.RTM."); while Freon 12.RTM. is a trademark of E. I. du Pont de Nemours & Co. Inc. for dichlorodifluoromethane, hereinafter "Freon 12.RTM." is used in this specification to denote dichlorodifluoromethane, regardless of the source) was the major, if not sole refrigerant, used in automobile air-conditioners, refrigerators, freezers and window air-conditioning units. Recently, however, Freon 12.RTM. has come under attack both nationally and internationally as an ozone layer-damaging chemical. In recent years, both the national and international scientific communities have linked Freon 12.RTM. with damage to the earth's protective ozone layer. Automobile air-conditioners, refrigerator/freezers and window air-conditioning units are believed to be a significant global source of ozone-damaging Freon 12.RTM..
In response to both scientific concern and a national and global outcry over the use of Freon 12.RTM. in air-conditioning, the United States Congress has acted to first reduce and then ban the use of Freon 12.RTM. in air-conditioning units.
One of the first areas in which the use of Freon 12.RTM. is to be phased out is in automobile air-conditioning. As a first step toward phasing out the use of Freon 12.RTM. in automobile air-conditioning units, Congress is phasing out the use of Freon 12.RTM. in new automobiles and has banned the sale of Freon 12.RTM. in small retail quantities for the do-it-yourself air-conditioner recharger market.
However, at the time of this application, the vast majority of automobiles in use in the United States contain Freon 12.RTM.-based air-conditioning units, and approximately 40% of new automobiles continue to contain Freon 12.RTM.-based air conditioners.
Prior to banning the retail sale of small quantities of Freon 12.RTM., owners of automobiles with Freon 12.RTM.-based air-conditioning units were able to recharge, or "top-off" the level of coolant in their automobile air-conditioners without the need for expensive professional service. Millions of units of Freon 12.RTM. recharging units were sold in the United States prior to being banned in January, 1994.
These Freon 12.RTM. recharger kits typically consisted of a 12 ounce (0.36 liter) aerosol can containing Freon 12.RTM.. The cans were fitted with an aerosol dispensing outlet that was compatible with a commercially available refrigeration manifold. In order to recharge an air-conditioning system, a customer needed to only fit the can to the manifold and discharge, or "drop in" the can's refrigerant charge directly into the air conditioning system, thus eliminating the need to bleed the system of existing Freon 12.RTM. before recharging.
Following Congress's ban on the retail sale of Freon 12.RTM. recharger kits, millions of automobile owners with Freon 12.RTM.-based air-conditioning units were left with no choice other than to seek expensive professional service to recharge their automotive air-conditioning units.
Also in response to Congress's ban on the use of Freon 12.RTM. in automobile air-conditioning, professional automotive service dealers began to retrofit existing Freon 12.RTM.-based air-conditioning units into new, non-Freon 12 refrigerant-compatible units.
The refrigerant authorized by the Environmental Protection Agency (EPA) to replace Freon 12.RTM. in automobile air conditioners is 1,1,1,2-tetrafluoroethane (hereinafter sometimes referred to as "134a" or "tetrafluoroethane"). Unfortunately, 134a has a markedly different temperature-pressure relationship at high operating temperatures than does Freon 12.RTM..
Because of this difference in the temperature-pressure relationship of Freon 12.RTM. and replacement 134a, existing Freon 12.RTM.-based systems cannot simply be bled of Freon 12.RTM. and refilled with 134a. Were Freon 12.RTM. to be replaced by 134a in a non-retrofitted Freon 12.RTM.-based air-conditioning unit, the unit could not be operated at high temperatures because the significantly higher pressure of 134a over Freon 12.RTM. would damage the unit. Hence, non-retrofitted, Freon 12.RTM.-based units that are simply refilled with replacement 134a are inoperative at high operating temperatures; thus, inoperative at precisely the time that air-conditioning is most desired.
Further, simply mixing 134a with existing Freon 12.RTM. in order to replenish, or "top off" the level of coolant is not feasible. When 134a is mixed with Freon 12.RTM., the mixture takes on the pressure characteristics of a higher pressure azeotrope, as opposed to Freon 12.RTM.. The temperature-pressure profile of 134a becomes markedly different from that of Freon 12.RTM. at temperatures within the high end of the normal refrigerant operating temperature range. Hence, replenishing lost Freon 12.RTM. with 134a in a Freon 12.RTM.-based air-conditioning system would lead to the same problems as the use of pure 134a in a non-retrofitted Freon 12.RTM.-based system: damage to the system caused by 134a's high pressure at high operating temperatures.
In addition, 134a is insoluble with the lubricant used in existing, non-retrofit Freon 12.RTM.-based systems. Thus, mixing 134a with Freon 12.RTM. in a non-retrofit Freon 12.RTM.-based unit leads to loss of lubrication and subsequent damage to the system.
Hence, in the absence of Freon 12.RTM. recharger kits, owners of automobiles with Freon 12.RTM.-based air conditioners face but one choice when the level of their air-conditioning coolant was low: professional service--at a significant cost--to remove the existing Freon 12.RTM., and retrofit the system to be compatible with 134a gas.
Prior to January 1994, owners of the millions of automobiles with Freon 12.RTM.-based air-conditioning units had a choice of whether to merely top off the level of air-conditioning coolant with an inexpensive do-it-yourself Freon 12.RTM. recharger kit or to undergo an expensive retro-fitting process. However, at the time of this application, owners of automobiles with Freon 12.RTM.-based air-conditioners no longer have this choice. They must undergo expensive professional maintenance, or discontinue the use and enjoyment of their automobile air-conditioners.
Thomas et al. (U.S. Pat. No. 5,254,280) discloses a lubricant developed for use with 134a and the combination of that lubricant with a refrigerant which is a replacement for R12. The lubricant contains polyoxyalkylene glycol, which is hydrophilic and will damage the system as discussed below.
Tamura et al. (U.S. Pat. No. 4,983,312) discloses a refrigerant blend similar to that claimed herein, but without a lubricant; it cannot be used in R12 automobile air conditioning systems, for the reason discussed below.
Systems that contain R12 are rarely produced today. New auto air conditioners use Refrigerant 134a. One sees R12 in older systems. These older systems have common components: R12, R12 mineral oil lubricant, and water that is sequestered into the dryer. If 134a were added to the system, it would damage the system as follows: (1) if no lubricant is added to the 134a (as in Tamura et al.), then the R12 system would be starved for lubricant, since the 134a gas is not miscible with the mineral oil lubricant; (2) if a synthetic lubricant is added to the 134a (as in Thomas et al.), then there is a different problem--that of moisture. Older systems have water trapped in their dryers. The synthetic lubricants (such as polyglycol- or polysiloxane-based lubricants) are hydrophilic. Thus, they are not only miscible with R12 and 134a, they are also partially or completely miscible with water. Thus, if they are introduced into an R12 system, they will pull this water out of the dryer into the refrigerant flow, initiating corrosion and damage to pressure switches and the TX valve. This is why Elf Atochem and DuPont publish elaborate flushing procedures and high efficiency dryer changeouts to prevent damage to the cooling system. There is also some concern with the compatibility of residual chlorine-bearing compounds on the 134a/blend lubricants (synthetic polyglycols and polysiloxanes).
Residual R12 vapors (CFC's) mixed with water yield hydrochloric acid fumes and hydrofluoric acid fumes. The dryer in a normal R12 air conditioning system contains a molecular sieve to trap moisture.
Wilczek, Gorski, and Anton of DuPont have patents on synthetic lubricants in various 134a and 134a/125 refrigerant systems. The DuPont patents discuss a gas known as 125 (pentafluorethane). 125 is five fluorine atoms bonded to an ethane molecule. This is a very large molecule for a refrigerant. It is not currently being produced, except as laboratory samples. Due to the nature of the molecular structure, the present inventor believes that the blend of 134a/125 will fractionate upon release to the atmosphere, as with a system leak. This fractionation will change the percentage composition of the blend and preclude its use in an automotive air-conditioning system where leaks are common.